1. Field
The present invention relates generally to medical treatment using convergent radiation, and more particularly to systems for planning and/or delivering such treatment.
2. Description
Conventional radiation treatment typically involves directing a radiation beam at a tumor located within a patient. The radiation beam is intended to deliver a predetermined dose of treatment radiation to the tumor according to an established treatment plan. The goal of such treatment is to kill tumor cells through ionizations caused by the radiation.
Healthy tissue and organs are often in the treatment path of the radiation beam during radiation treatment. The healthy tissue and organs must be taken into account when determining a treatment plan. Specifically, the treatment plan must strike a balance between the need to minimize damage to healthy tissue and organs and the need to ensure that the tumor receives an adequately high dose of radiation. In this regard, cure rates for many tumors are a sensitive function of the radiation dose they receive.
It is therefore desirable to design treatment plans that maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. In conventional radiation treatment systems, a linear accelerator generates a divergent beam of photons having energies in excess of 1 MeV and the beam is directed toward a target within a patient. A conventional treatment plan may call for shaping the beam with beam shaping devices to conform to the target and to avoid healthy tissue. A dose delivered by a conventional megavoltage system reaches a maximum at a tissue depth that depends on the energy of the delivered photons. Accordingly, conventional treatment plans also call for photons having energies corresponding to the depth of the target.
A kilovoltage radiation treatment system such as those described in U.S. Pat. No. 6,366,801 to Cash et al uses a radiation source which produces a divergent beam of traditional medical x-rays having energies in the 50 to 150 keV range and focuses the beam on a target using a lens designed for this purpose. Conventional planning systems such as those described above are not suitable for these treatment systems because the characteristics of the focused beam are quite different from those of conventional megavoltage radiation. For example, the focused beam follows a convergent, rather than a divergent, path. Also, while absorption of the megavoltage radiation may be considered dependent primarily on the density of tissue through which it passes, absorption of the focused beam is highly dependent on tissue composition.
Moreover, as described in Cash, kilovoltage radiation may be used to irradiate a tumor that has been injected with a contrast agent composed of heavy elements. The tumor thereby receives a larger radiation dose than it would have received without use of the contrast agent. Contrast agents are not commonly used in conjunction with megavoltage radiation treatment, therefore conventional treatment planning systems are also not suitable for planning treatments in which tumors injected with contrast agent are irradiated by kilovoltage radiation.
To address at least the foregoing, some embodiments of the present invention provide a system, method, apparatus, and means to determine a treatment plan for delivering convergent radiation to a target based at least on a decrease in intensity of the convergent radiation due to material intercepted by the convergent radiation prior to reaching the target and on an increase in intensity of the convergent radiation due to a geometry of the convergent radiation. Some aspects include determination of a dose enhancement at the target over time due to contrast agent located at the target, wherein the determination of the treatment plan is based at least on the dose enhancement over time.
In other aspects, a system is provided having a radiation source for emitting radiation, a radiation-focusing lens for substantially focusing the radiation on a target, and a processor for determining a treatment plan for delivering convergent radiation to a target based at least on a decrease in intensity of the convergent radiation due to material intercepted by the convergent radiation prior to reaching the target and on an increase in intensity of the convergent radiation due to a geometry of the convergent radiation. According to some aspects, the system further includes a contrast agent delivery unit for placing contrast agent at the target, and an imaging system for generating data representing a decrease in the contrast agent at the target over time, wherein the determination of the dose enhancement over time includes a determination of a decrease in the contrast agent at the target over time based at least on the data representing the decrease in the contrast agent.
Some aspects of the invention include determination of an energy distribution profile of radiation convergent on a target by a radiation-focusing lens, acquisition of data representing material between the radiation-focusing lens and the target, determination of a decrease in intensity of the convergent radiation at the target due to the material and based on the energy distribution profile, determination of an increase in intensity of the convergent radiation at the target due to a geometry of the convergent radiation, and determination of a treatment plan based at least on the decrease in intensity of the convergent radiation at the target due to the material and the increase in intensity of the convergent radiation at the target due to the geometry of the convergent radiation. Further to these aspects, also provided may be determination of a decrease in contrast agent at the target over time, and determination of a dose enhancement function based at least on the decrease in the contrast agent at the target over time, wherein the treatment plan is determined based at least on the dose enhancement function.
The present invention is not limited to the disclosed embodiments, however, as those of ordinary skill in the art can readily adapt the teachings of the present invention to create other embodiments and applications.